Lead screw operated potentiometer



NOV. 26, 1968 s GREENE 3,413,589

LEAD SCREW OPERATED POTENTIOMETER Filed sept. v, 1965 .o .ai ,7

United States Patent G 3,413,589 LEAD SCREW OPERATED POTENTIOMETERSanford I. Greene, Wantagh, N.Y., assignor to Fairchild Camera andInstrument Corporation, a corporation of Delaware Filed Sept. 7, 1965,Ser. No. 485,357 2 Claims. (Cl. 338-180) ABSTRACT F THE DISCLOSURE Alead screw operated potentiometer comprises a housing having alongitudinal cavity with the side walls forming guide surfaces. In thecavity are disposed an elongated resistance element, a longitudinallymovable carriage carrying a resilient contact Ushaped in cross-section,and a lead screw. The lead screw engages complementary threads orgrooves in the carriage extending only for 180 or less. As the leadscrew is rotated, it exerts a downward camming action on the carriage,biasing the contact into engagement with the resistance element. In theevent it is attempted to drive the carriage beyond its limit of travel,the lead screw cams the carriage out of engagement with its threadsagainst the resilience of the contact element, thereby constituting anautomatic overload release clutch.

Background of the invention This invention relates to lead screwoperated potentiometers and particularly to such potentiometers of thetype in which a resilient contact element serves both to bias itscarriage into engagement with the leadA screw and to act as an overloadrelease clutch.

There have heretofore been marketed and proposed numerous lead screwpotentiometer mechanisms. In general, these have comprised some form ofcarriage positively engaging the lead screw for axial movement upon itsrotation and a resilient contact element supported by such carriage forengaging a resistance element disposed parallel to the lead screw. Dueto the positive engagement of the contact carriage and the lead screw,the device is subject to damaging in the event longitudinal movement ofthe contact carriage is jammed or obstructed, for example' by an attemptto move it beyond its limit of travel.

It is an object of the invention, therefore, to provide a new andimproved lead screw operated potentiometer which obviates theabove-mentioned disadvantage of prior devices of this type.

It is another object of the invention to provide a new and improved leadscrew operated potentiometer in which the contact carriage is biasedinto engagement with the lead screw by the contact element so that itserves as an overload release clutch.

Summary of the invention In accordance with the invention, there isprovided a lead screw operated potentiometer comprising a housing memberfor containing the operative elements of the potentiometer and includingtwo opposed parallel guide surfaces having opposed longitudinal guideslots, a lead screw rotatably mounted within the housing parallel to itsguide surfaces and including a portion accessible from the exterior ofthe housing for rotating the same, a resistance element supported in thehousing parallel to the lead screw, a resilient sliding contact engagingthe resistance element and having lateral extensions riding in the guideslots of the parallel guide surfaces, and a carriage for the contacthaving longitudinal and transverse sliding engagements with the parallelguide surfaces and having a plurality of transverse groovescomplementary to substan- 3,413,589 Patented Nov. 26, 1968 ACe tialportions of the threads of the lead screw and engaging the same over asubstantial arc not greater than -facing the resistance element, wherebythe resilient contact serves to bias the carriage into engagement withthe lead screw and to permit disengagement therefrom if it is attemptedto drive the carriage beyond its limit of travel, thus forming anzautomatic overload release clutch. The term potentiometer is usedherein and in the appended claims in accordance with its ordinary tradeusage, referring to a resistance element with a sliding contact.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription, taken in connection with the accompanying drawing, whileits scope will be pointed out in the appended claims.

Referring now to the drawing:

FIG. 1 is a longitudinal view, partly in section, of a lead screwoperated potentiometer embodying the invention, the sectionalizedportions being taken along the linel 1-1 of FIG. 2;

FIG. 2 is a cross-sectional view of the potentiometer of FIG. 1 alongthe line 2 2; while FIG. 3 is an exploded perspective view, partlybroken away, of the contact assembly of the potentiometers of FIGS. 1and 2.

Referring now more particularly to FIGS. 1 and 2 of the drawing, thereis represented a lead screw operated potentiometer embodying theinvention comprising a housing member 10 for containing the operativeelements of the potentiometer and including two opposed parallel guidesurfaces 10a, 10b having opposed longitudinal guide slots 10c and 10dformed therein. A lead screw 11 is rotatably mounted in the housingmember 10 as in sleeve bearings 12 and 13. As shown in FIG. 2, the leadscrew is disposed parallel to the guide surfaces 10a, 10b and includes aportion 11a, such as an extension of the root diameter of the leadscrew, provided with a screwdriver slot accessible from the exterior ofthe housing for rotating the lead screw.

The potentiometer of the invention further comprisen an elongatedresistance element 14, shown in the form of a wire-wound element,supported in the housing member 10 parallel to the lead screw. Thepotentiometer further includes an elongated contact element 15, shown inthe form of a conductive rod, supported in the housing parallel to theresistance element 14.

The potentiometer further comprises a resilient sliding contact element16 including a pair of extending resilient arms 16a and 16b, the arm 16aengaging the resistance element 14 and the arm 16b engaging the contactelement 15. The element 16, with its arms 16a and 16b, has a U-shapedcross-section, as indicated. The contact element 16 also has lateralextensions 16e and 16d which ride iu the guide slots 10c and 10d,respectively. The main portion of the contact element 16 is providedwith a pair of holes 16e and 161 for a purpose described hereinafter.

The potentiometer of the invention further comprises a carriage 17 forthe contact element 16 and having a pair of protrusions 17a and 17b fordetachably engaging the holes 16e, 16f, respectively, of the contactelement 16. As shown more clearly in FIG. 3, the carriage 17 is ofapproximately U-shaped cross-section, the outer `arms of which havelongitudinal sliding engagements with the guide surfaces 10a, 10b of thehousing member 10. The carriage 17 has a plurality of transverse groovesor threads 17c in the base of the U, substantially complementary to andengaging substantial portions of the threads of the lead screw 11 over asubstantial arc not greater than 180, and preferably approximately 180,on the side of the lead screw 11 facing the resistance element 14.

As shown more clearly in FIG. 1, the 4grooves or threads in the carriage17 engage substantial portions of the threads of the lead screw 11 butnot the entire threads as in an ordinary` threaded engagement. Thepotentiometer will also be provided with conventional externalelectrical terminals connected to the contact rod and to the terminalsof the resistance element 14 (not shown). As shown, the carriage 17 isof insulation material but if it is permissible that the head 11a oflead screw 11 be at the potential of the sliding contact 16, thecarriage 17 may be of a conductive metal and the lead screw 11 used asthe electrical connection to the contact 16, in which case the contactrod 15 may be omitted. An enclosing cap 18 is secured to the end of thehousing member 10 as by suitable screws 19 to retain the parts in theirassembled positions.

It is `believed that the operation of the lead screw operatedpotentiometer of the invention will be apparent from the foregoingdescription. In brief, rotation of the lead screw 11 by its extension11a causes the carriage 17 `and the contact element 16 to movelongitudinally, varying the amount of the resistance between the contact16a and the terminals of the resistance element 14 in a conventionalmanner. During this movement, the outer faces of the U-shaped carriage17 slide along the guide surfaces 10a, 10b of the housing member. InFIG. l, the parts are shown with the carriage 17 and contact 16 at theirextreme left-hand positions. If, now, it were attempted to move theseelements still further to the left by further rotation of the lead screw11, the camming action of the lead screw on the threads or grooves ofthe carriage 17 would force it downwardly against the bias of theextensions 16e and 16d of resilient contact element 16 which bear on thelower faces of the guide slots 10c and 10d, respectively, as shown inFIG. 2, disengaging the lead screw from the carriage 17. During thismovement, the outer surfaces of the carriage 17 would slide verticallyalong the guide surfaces 10a, 10b, that is, transverse to the normalsliding movement.

The lead screw operated potentiometer described has a number of distinctadvantages over prior devices of this type. The carriage 17 can bereadily molded from a thermosetting resin since the threads 17c do notextend over 180 of arc so that the upper half of the threads arecompletely open. Further, the carriage 17 engages the lead screw with aplurality of threads over approximately 180 of arc, thereby reducing anddistributing wear and assuring long life and reliability. Thisconstruction is to be contrasted with some prior designs in which asingle wire or lbail on the carriage engages a single thread of the leadscrew. The camming .action of the threads of the lead screw on thegrooves of the carriage 17 is such as to assist in biasing the contacts16a, 16h into engagement with the resistance element 14 and the contact15, respectively, assuring positive electrical contacts. Moreover, asdescribed above, the carriage 17 :and contact 50 element 16 serve as anoverload release clutch, preventing damage to the device.

While there has been described what is, at present, considered to be thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein, without 4 departing from the invention, and it is, therefore,aime in the appended claim-s to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A lead screw operated potentiometer comprising:

a housing member for containing the operative elements of thepotentiometer and including two opposed parallel guide surfaces havingopposed longitudinal guide slots;

a lead screw rotatably mounted within said housing parallel to saidsurfaces and including a portion accessible from the exterior of saidhousing for rotating the same;

a resistance element supported in said housing parallel to said leadscrew;

a resilient sliding contact engaging said resistance element and havinglateral extentions riding in said guide slots;

and a carriage `for said contact having longitudinal and transversesliding engagements with said surfaces and having `a plurality oftransverse grooves complementary to substantial portions of the threadsof said lead screw and engaging the same over a substantial arc notgreater than 180 facing said resistance element;

whereby said resilient contact serves to bias said carriage intoengagement with said lead screw.

2. A lead screw operated potentiometer comprising:

a housing member for containing the operative elements of thepotentiometer and including two opposed parallel guide surfaces;

a lead screw rotatably mounted within said housing parallel to saidsurfaces and including a portion accessible from the exterior of saidhousing for rotating the same;

a resistance element supported in said housing parallel to said leadscrew;

a resilient sliding contact engaging said resistance element andincluding a plurality of holes;

and a carriage including a plurality of protrusions detachably engagingsaid holes in said sliding contact to actuate the same, havinglongitudinal and transverse sliding engagements with said surfaces andhaving a plurality of transverse grooves complementary to substantialportions of the threads of said lead screw and engaging the same over asubstantial arc not greater than facing said resistance element;

whereby said resilient contact serves to bias said carriage intoengagement with said lead screw.

References Cited UNITED STATES PATENTS 2,926,324 2/1960 Barden et al.338--180 3,187,289 6/1965 Rolwes 338--180 3,238,488 3/1966 Laugenbach etal. 338-180 RICHARD M. WOOD, Primary Examiner.

I. G. SMITH, Assistant Examiner.

